The invention relates to a process for the production of a shaped sheet metal piece with different material thicknesses according to strength and stiffness requirements by deep-drawing.
The generic production process is used in particular for lightweight construction and especially in the production of motor vehicle bodies. While in the past it was conventional to design a shaped sheet metal piece in its thickness according to the area/section of highest mechanical requirements, in the meantime there has been a transition to differentiation with respect to material thicknesses relative to the locally different stiffness requirements.
A corresponding process is described for example in DE 43 07 563 C2. The patent explains a process for the production of a sheet metal structural part which has a multiple sheet structure consisting of a base sheet and in places a stiffening sheet or several stiffening sheets joined to it, the base sheet and the stiffening sheet or stiffening sheets being jointly deep-drawn. Here the stiffening sheet or stiffening sheets is or are at least partially attached to the base sheet and are permanently joined to the base sheet after deep-drawing.
One corresponding procedure is described in patent application DE 42 28 396 A1, in which in addition to a partial increase in stiffness a further objective is to reduce the oscillatory mass of flat or slightly deformed areas of the sheet metal piece and thus to increase the eigenfrequencies.
The aforementioned prior art is subject to the disadvantage that such a procedure requires relatively high expenditures with respect to production and logistics.
EP 0 486 093 B1 describes a process in which the reinforcement of partial areas of a shaped piece is done by means of a reinforcing structure element which is formed separately from a plate body to be covered and which is only subsequently joined to the likewise completely formed plate body. In this procedure the forming process is complicated and expensive.
For the sake of completeness reference is made to DE 41 04 256 A1. There, using in particular the example of body parts for passenger cars and trucks, it is explained how the highly loaded local areas (hinge seats, lock reinforcements, attachment areas for sleepers and other bearing parts) can be effectively reinforced. As a result, in this process shaped pieces are produced which have also become known as so-called "tailored blanks" (see in this regard also VDI-Reports [Association of German engineers] No. 1002, 1993, pages 45-51). In the latter citation it is shown especially using the example of inside door sheet metal how sufficient stiffness can be achieved by larger sheet metal thicknesses in the area of the hinge and lock attachment. A reduction in weight results in the thin sheet metal placed between thicker sheets. It is disadvantageous in these sheets that they can essentially only be used for shaped pieces which are not visible on the finished product. The two aforementioned publications are explicitly geared to shaped bodies which are either themselves an inner part of a combination of parts or which are reinforced by separate shaped pieces on one partial inner surface with disturbance of the outer surface.
The object of the invention is to devise a further process for the production of a shaped sheet metal piece with different material thicknesses according to strength and stiffness requirements which can be executed economically and without problems with respect to the forming process.
The approach as claimed in the invention is shown in the process features according to the characterizing part of claim 1. A shaped sheet metal piece produced in this way requires only relatively low additional production and logistic expenditures. The shaped sheet metal pieces are characterized by high surface quality and smooth transitions between the areas of differing material thicknesses.
Heating in the area of the forming for deep-drawing of steel sheets, especially austenitic steel sheet, is inherently known from DE 23 32 287 B2. In the area of force transfer on the other hand cooling takes place. Heat treatment is generally used to configure the deep-drawing process such that austenitic steel sheets can be formed. Heat treatment which varies over the surface of the sheet blank with the object of this invention, i.e., to obtain material thicknesses which differ according to strength requirements, does not take place.
Furthermore, DE 44 25 033 A1 discloses a process and a device for compression forming of workpieces, a workpiece being clamped in a clamping device and being formed by at least one compression tool. In particular there is a laser beam means which causes the workpiece to be exposed to the laser beam and heated in order to reduce flow stress and improve the capacity for deformation. The forming temperature can be adapted to different materials and can be controlled. In this way local heating of the workpiece can take place in the areas of high degrees of forming. In various embodiments it is also possible to reduce the wall thickness of the workpiece without detailing why this reduction is desirable.
DE 43 16 829 A1 furthermore describes a process for material working with diode radiation, in which the beam profile can be matched to the machining process. Possible applications include: forming and bending of a workpiece, laser beam flame cutting, welding of workpieces, removing impurities or coatings from workpieces, local heating for support of metal cutting on workpieces and soldering of workpieces.